Thanks for sharing your boilers Raphael, yes there are a lot of boilers on the market that are much cheaper than Stuart's offerings. The only other equivalent of the babcock boiler on offer to my knowledge is the Cotswold 'Thor' boiler which is much smaller than the 504, however i'm sure a good boilermaker could easily make one up.
That being said i have no doubts the new Stuart 504 will sell well for them.